Relativity
by wickedfanzel
Summary: Beckett's cousin comes to visit and sets in motion a series of events to finally get Castle and Beckett together.
1. Chapter 1

**Author's Note:  
>This my first fanfiction ever so please be gentle.<br>This is set sometime in Season 4 and slightly AU. ****Set before 47 Seconds.  
>I know that Alexis has been very resentful towards Beckett this season, but in this story, Alexis will be more accepting towards Beckett than she is on the show. <strong>

**I originally started writing this between Seasons 2 and 3 and I just recently came back to it. I've updated this a lot from what I originally had to reflect events of Season 4. Any and all mistakes are mine.**

**Summary: Kate's cousin Liz comes to visit during spring break and sets in motion a series of events to finally get Castle and Beckett together. **

**Disclaimer: All characters and other aspects of this story (except Liz) are not mine.  
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Monday morning at the Castle household started like it always did. Alexis preparing for a day following Lanie; Martha practicing lines for her next play; and Castle getting ready for another day shadowing Detective Kate Beckett. As her son left the loft Martha couldn't help but wonder when he was going to act on his feelings for the detective. For all of their sakes, she hoped things would progress sooner rather than later. Little did she know that today would be the day that set things in motion for something more between a certain writer and his muse.

When he arrived at the precinct, Castle immediately sensed that something was different. Everyone was smiling and laughing not the normal atmosphere at the 12th. As he walked over to Beckett's desk he noticed a strange young woman sitting in his usual seat and an unusually happy detective.

"Speak of the devil." said Kate.

The strange young woman turned around and almost leapt out of her seat at the site of The Richard Castle walking toward her. While he was used to that reaction, he was not expecting her to walk up to him with the air of confidence and familiarity that she had. Most women were flustered and nervous when they first met the famous author.**  
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>"So you're Richard Castle huh?" said the strange young woman.<p>

"Yes….?" said Castle.

Before the moment could get any more awkward, Kate came to the rescue: "Castle, I'd like you to meet my cousin Elizabeth."  
><em><br>Ah! So that explains her strange reaction to me. She's Beckett's cousin._Castle thought to himself.

"But everyone calls me Liz." interjected Liz.

"It's a pleasure to meet you…. I've heard absolutely _nothing_ about you."

"Well that's funny, I've heard a lot about you. " Said Liz turning to Kate "Why haven't you told your writer boy about your favorite cousin Katie?"

Seeing that Castle was about to make a comment about the whole "Katie" thing Beckett cut him off: "Don't even think about calling me Katie, Castle."

"Whoa, how did you know what I was going to say?"

"Because after having you shadow me around for the past few years I'm getting really good at predicting what you're about to say at any given moment."

Castle and Beckett continued to argue like this for a few minutes while Liz watched with an amused look on her face. After hearing everything Kate had said about her unconventional partner/favorite author who was basing a series of books off of her, she had quickly come to the conclusion that Kate was falling for him whether she realized it or not. Now seeing the two of them together, it was not hard to deduce that the feeling was mutual. She had been plotting for weeks how to give them both a push in the right direction. The only question was how to get these two very stubborn people to admit they were in love with each other.

"So Liz, what brings you to the 12th precinct on this fine day?" asked Castle

"I usually visit Kate in the city over the summer, but I couldn't this year because she was shot, so I'm here for spring break instead. I don't get to see my favorite cousin as much as I would like to and now I have a chance to see how she's getting along with you along for the ride." Liz replied.

Castle turned to Kate, "How come she gets to hear all about me but I didn't even know you had a cousin?" He pouted.

Kate rolled her eyes. "I wanted to keep some mystery to Nikki Heat. I didn't want to put everything out there all at once, you know? Keep the fans wanting more…Isn't that what all good writers do? Leave some questions unanswered so the reader will have to pick up the sequel or sequels to find out more about their favorite characters?" She smiled.

Sensing it was better to keep quiet to see where this went, Liz watched the two of them bicker/flirt back and forth until she saw Kate's best friend and favorite ME walk into the precinct.

"Hey Lanie!" shouted Liz.

Kate and Castle both jumped. They had been so wrapped up in their "argument" that they had become oblivious to the world.

"Hey Liz," said Lanie, "How you doing girl?"

"I'm doing well. It's nice to be back here again. Things sure have changed around here. It's so strange not to see Captain Montgomery at his desk."

At this, everyone looked over at the captain's office reflecting on all that had been lost all those months ago.

"Yes they have." Lanie replied giving Kate and Rick a look. "What do you think of the new captain?"

"She's ok. She didn't seem to thrilled to have me here though since I'm a civilian." Liz replied.

"Don't worry about that kid." Castle said, "She still hasn't warmed up to me even with my charm and ruggedly handsome looks." At this, the three women laughed.

Gates stuck her head out of her office, "What's going on out there? Don't you have a case to solve?"

"Yes Sir!" Beckett replied, "We'll get right on that."

Castle turned to Lanie. "What are you doing at the precinct? Shouldn't you be cutting up some dead guy?" Castle asked.

"You know Castle I do have a life outside of cutting up dead people. Sometimes it's nice to talk to someone who actually responds when you talk to them." She turned to Kate, "I'm actually here to tell you about what I found during the autopsy of your latest vic."

Lanie and Beckett walked off to talk about the latest autopsy leaving Castle and Liz alone.

"So Liz can I ask just how you and Beckett are related?"

"I guess. Johanna and my father were siblings. Aunt Jo was 5 years older than my dad. My dad adored her. When we found out she had been killed he was devastated. I was only 10 at the time. Kate was 20. She had the whole world at her disposal and then her world was shattered. She had just come back from a semester in Russia a few months before. It took her a long time to get herself… and my uncle back together and on solid ground."

"What was she like?"

"She was the best aunt a girl could ask for and an amazing mother to Katie. She was always fighting for the little guy. She and Kate were really close. Since I was only ten when she was killed, my dad tells me stories about her to this day to make sure never forget her. I know it's hard for Uncle Jim and Katie to talk about Aunt Johanna so my parents and I only talk about her if Kate or Uncle Jim mention her. I really miss her."

"She sounds like a wonderful woman. I wish I could have met her." Castle replied.

"Oh she would have loved you, after she gave you the third degree of course. Aunt Johanna was always the one who got to intimidate Kate's dates. Uncle Jim was the nice one."

At that comment, Castle choked and started coughing. Liz hadn't been at the funeral on that fateful day, so there was absolutely no way she could know about his confession. That raised the question in his mind if Kate ever said anything to Liz about her own feelings towards him. Was it possible that she felt the same?

He quickly squashed that thought as wishful thinking. But the memories of her looks and attitude toward him especially over the last few weeks stirred some hope within him that maybe, just maybe, Beckett's wall was coming down faster than he had hoped for.  
>He was a little freaked out that this young woman who he had just met seemed to have such an insight into his partnership with Beckett.<p>

To cover his confusion he asked,"What do you and Beckett usually do when you visit? Girls' nights? Shopping sprees? Gossip about boys?"

Liz couldn't help laughing. "We usually spend some time catching up on what's been happening. Since I'm usually here in the summer, we'll go jogging in Central Park or go to a museum. We also like to take a drive out of the city and visit this amazing store that sells all sorts of things, used books, antiques, cool paintings, and other really neat stuff. That's where she got a lot of the awesome stuff in her apartment after the other one blew up. Thanks for pulling her out by the way."

"Uh, no problem." Castle stuttered. She really did know a lot about what happened to Kate since he had started following her.

"I really want to make this visit with Kate special this year since we came so close to loosing her. After the shooting, the reality of her being a cop hit home for me. She would never talk about life threatening situations that she had been in with me, so I never really thought about just how dangerous her job really is until now."

Castle could certainly relate to that. He had seen the life draining out of her while they waited for the ambulance to arrive at the cemetery and didn't want to repeat that scenario any time soon. An image of his murder board back at the loft flashed in his mind. That was why he hadn't yet told Kate about his side investigation into her mother's murder, he couldn't bear the thought of her being taken away from him permanently.

"So, any ideas on how you're going to make this year special?" Castle needed to get his mind on more positive things. "I'd be willing to pitch in if you need any financial help to pull whatever it is you're planning off." He didn't need to add that he was willing to do anything to make Kate happy. He loved seeing her smile. Liz gave him a knowing look. Yeah, he was head over heels in love with her cousin all right.

"That would be amazing! Thanks Mr. Castle! I have some ideas, but I'll let you know if I need any help."

"Please call me Rick, or even just Castle would be fine Liz. You're Beckett's cousin. Mr. Castle just seems to formal."

"Oh, ok. Great! Thanks." Liz smiled. Kate really knows how to pick them she thought to herself.

Suddenly Alexis came around the corner. "Hey Dad!"

"Hey pumpkin! How's Lanie treating you?"

"She's great! I'm really enjoying working with her. The dead bodies aren't too bad."

"Alexis, this is Detective Beckett's cousin Liz. She's spending the week with her."

"It's nice to meet you Liz."

"It's nice to meet you too Alexis. Kate mentioned you a few times. I don't think I would be able to work with Laine down in the morgue. Weak stomach." Liz faked gagging.

Alexis laughed" I like interning for Dr. Parish. It's fun to see a little of what my dad's been doing for the past few years. It really gives me an appreciation for why he enjoys this so much. And I get to see my dad in action solving crimes, which is kinda cool. It's also amusing seeing Detective Beckett keep him in line. She's really good at putting up with my dad every day."

Just then Beckett popped her head around the corner. "Castle, you have to see what Lanie found on the body."

Castle jogged away without a backwards glance.

Alexis rolled her eyes. "He's like a puppy." Liz observed.

While Castle was out of earshot, Liz turned to Alexis. "Do you think they'll ever admit that they are in love with each other?" she asked.

"I really hope so. I've never seen my dad this happy. Ever since he started following her around, he's been different. I mean, I do get annoyed with the way she treats him sometimes. It was hard on him this past summer when she didn't call him for three months. I could tell that he was back working with her in September without him having to tell me though. He was so happy to be back in her presence."

"It's the same with Katie. She's always so happy these days. She acts like he annoys the Hell out of her but she enjoys his company and insight into her investigations. She's told me that half of the cases he's helped her on she never would have solved without him. She might not even notice that I'm here this week." She pouted and then laughed. Liz quickly filled Alexis in on the reason for her trip to visit Kate during spring break instead of during the summer like usual.

"So I wanted to make this week extra special for her because we missed out on our week last summer." Liz concluded.

Suddenly Alexis got an idea: "I just got a great idea. What if you and Kate came over for dinner on Friday? You said yourself that my dad makes her happier."

"That's a great idea Alexis! Do you think you can persuade your dad?"

"Piece of cake. He'll do anything to spend more time with her."

"And while we're at it we can plot how to get them to admit their feelings to each other." Liz grinned

Suddenly Castle and Beckett appeared.

"Hey Alexis. I see you've met Liz," said Beckett.

"Yeah, she's really nice." Alexis replied.

"Liz isn't preventing you from working is she?"

"No! Liz is great. We have a lot in common." Liz smirked at Alexis.

"Listen we just got a lead about on this case, so we have to go check it out. Will you be Ok here?" Beckett looked at Liz

"Yeah Katie I'll be fine. I'm a big girl now remember. I'll stay go back to the ME's office with Alexis and Lanie and not actually go into the morgue."

"All right. We'll be back in a few hours. See you then."  
>As soon as they were out of earshot Alexis turned to Liz, "I'll talk to my grandmother tonight. She wants to see them happy as much as we do. I'm sure she'll come up with some creative ideas."<p>

"You're grandmother is Martha Rogers right?"

"Yeah, that's her."

"I can only imagine what she might come up with."

"I'll try to keep her from doing anything too over the top."

Before they could make any more plans, Lanie walked up to take them to the morgue while they waited for Kate and Rick to return. Without hesitation, the girls filled Lanie in on their plan. If anyone could help them get ideas, it was Kate's best friend. The ME immediately volunteered to help with any prep work that might be needed.

**AN:  
>So that's the end of Chapter 1. I already have most of the next two chapters written and they will be up within a week.<br>****Please review and let me know what you think!**


	2. Chapter 2

**Author's Note:  
>First of all, thank you all for your reviews, story alerts, etc. I am overwhelmed by the response that I've gotten for this. I never expected such a response. <strong>

**One reviewer asked about Liz's age and to clarify, she's 21 years old in this story. So she's on spring break from college and visiting Kate. Hopefully that clears things up. **

**Disclaimer: A****ll characters and other aspects of this story (except Liz) are not mine.**

**And now without further ado, on with the story!**

On the ride over to the ME's office Lanie offered the two younger women suggestions for how to best make their plan, dubbed Operation: Caskett work. It was agreed that Alexis would talk to her dad and Liz would talk to Kate about the other and try to get them to confess their feelings before Friday night. Liz and Alexis would also plant the seeds of hope that their feelings were reciprocated.

When Beckett and Castle returned to the ME's office 3 hours later to collect Liz and Alexis, both girls had a plan worked out in their heads for how they would broach the subject. Phone numbers had been exchanged and code words decided on in case they were unable to talk freely.

Later that night, Alexis approached Martha about the plan she and Liz had come up with.  
>"Oh my dear, that's a great idea! Hmm… now how to get them alone and actually in the mood to talk about how they feel."<p>

"Try to be subtle Gram. We don't want them thinking they've been set up."

"Of course dear. What if we… oh wait no that would be too 'over the top' as you would say."

Alexis laughed. "I'm sure you'll think of something."

"What are my two favorite ladies plotting now?" Castle asked as he walked into the room.

"I was just telling Gram about something Liz told me today."

"Oh yeah? What's that sweetie?"

" Liz told me that she wants to make this week with Detective Beckett special and Gram and I were thinking about asking her to come here for dinner that night. We can invite her dad and Liz too."

"That's very sweet of you Alexis, but I think Liz probably meant that she wanted to do something special with just the two of them." Castle could tell how much happier Beckett seemed having her cousin in town and he didn't want to ruin that by forcing her to spend more time with him, not that he would mind spending more time with her.

"Are you kidding Dad? Beckett enjoys spending time with you and you enjoy spending time with her. Having her over for dinner would be a win/win situation. And besides, I already mentioned the idea to Liz and she was all for it!" Alexis protested.  
>Castle nodded reluctantly. <em>At least the cousin agrees with this idea. If the night turns into a disaster, at least it won't be my fault entirely. <em>Castle thought to himself.

As soon as she saw her father nod his head, Alexis added "And you should probably be the one to invite her since you're the one who knows her best."

"Well if you're both OK with it, I'll mention it to her tomorrow." Castle said reluctantly. He was excited about the prospect of having Beckett over to the loft for dinner along with the other members of her family. At least with Liz and Jim along as well this wouldn't seem like a date, although for some reason, he couldn't help picturing such a scenario with just him and Kate without their families present.

Alexis and Martha exchanged an excited look as he walked out of the room with a new bounce in his step.

The next morning at the precinct, a very nervous Castle approached Beckett's desk with coffee in hand. Kate immediately perked up when she noticed Castle and coffee coming her way.

Seeing how nervous Castle was made Liz break into a huge grin. _Yes! Go Alexis! _Right on queue, Liz's phone rang showing Alexis calling. "Hey, would you look at that. It's Alexis. I'll be right back." She practically sprinted out of the room.

Castle and Beckett watched her go with slightly bemused expressions on their faces.

"Well they seem to have bonded quickly." said Kate

"A little too quickly if you ask me." Castle replied.

"Are you all right Castle? You seem a little nervous. You didn't commit any murders did you?" Beckett smiled.

"If I did would you spank me?" Castle raised his eyebrow suggestively. Kate rolled her eyes as he sat in his usual seat.

"Spit it out Castle."

"So Be- Kate, I was wondering… Are you busy this Friday night?"

"I'm not sure. It all depends on Liz. She has a secret agenda for me on Friday. I have no idea what she's going to force me into doing. She's not usually so secretive about her plans. I'm not allowed to know anything, which is unusual. She's not usually so secretive about her plans. Anyway, why do you ask?"

"Well, I was wondering if you would like to come over to my place on Friday evening to have dinner with me and my family" At her raised eyebrow, he quickly added, "Your father and Liz are invited too of course!"

Kate looked over at him and saw a mix of emotions on his face nervous, excited, and hopeful. She contemplated messing with his head a little, but the look on his face gave her pause. She couldn't do that to him, he looked like a puppy. "Yeah, I would like that." She replied looking at him with warmth in her eyes. "Just out of curiosity why are you asking me to come to your house this Friday? It seems kind of out of the blue."

Castle hesitated. _Because I love you_ were the words that he wanted desperately to say. Instead he replied, "Alexis mentioned the idea to me last night. And since it looks like Alexis and Liz are really hitting it off and I thought it would be nice to have everyone over for a fun night." _Yeah, it was Alexis' idea. She can't possibly refuse knowing that my daughter was the one who had the original idea._

Liz had been lurking around the corner and keeping an eye on how the conversation was going. Seeing both of them smiling was a good sign. She casually walked back over to the duo trying to act nonchalant.

When she saw her cousin headed back toward them, Kate was jolted back to reality and out of her fantasy of what dinner with just herself and Castle would be like.

"Lizzy, I know you already had plans for us on Friday, but Castle just invited all of us to his loft for dinner on Friday night. Do you think you would be able to work that into your mysterious schedule for the day?" Kate asked. She was trying to remain neutral in her tone, but Liz detected a little bit of pleading in her voice. She really wanted to do this.

"That's funny. Alexis was just mentioning that invitation to me over the phone. Dinner sounds like fun. Let's do it!" Liz was trying to remain calm on the outside while on the inside she was jumping for joy that everything was going according to plan so far.

Unfortunately, the internal excitement was too much and as Liz went to hug her cousin, the combined weight was too much for the chair Beckett was still sitting on. With a crash, the chair fell backwards with Kate and Liz landing in a heap.

Castle was torn between concern for his partner and amusement at her predicament. The absurdity of what had just happened caused amusement to win over and he could no longer contain his laughter.

"Are you just gonna stand there and laugh or are you going to help us up?" the annoyed and somewhat amused voice of Kate Beckett floated up from the floor.

Castle quickly sobered and reached down to help the cousins up from the floor. He helped Liz up first and then reached down to grab Kate's hand to pull her up. Kate pushed herself up just as Castle pulled which caused Castle to misjudge the amount of force necessary to pull her up and she ended up crushed into his chest. For a few seconds, they stood like that with their faces inches from the other's staring into each other's eyes. Castle's eyes dropped down to her lips for a split second and he flashed back to that night last January when they had kissed. Beckett noticed how his eyes darted to her lips and she shivered with the memory of just how incredible it felt to kiss him.

"Hey Liz!" "What's up girl?" Ryan and Esposito entered the bullpen shattering the moment.  
>Castle and Beckett quickly jumped apart.<br>_  
>Damn! If Ryan and Esposito hadn't come in when they did, we might not have had to find a way to leave them alone on Friday. <em>Liz wanted to scream with frustration. Instead she ran over to the boys and hugged both of them. "Hi! Long time no see!"

While Liz greeted Ryan and Esposito, Castle and Beckett were still recovering from what had nearly happened. Beckett refused to meet his eyes and Castle was trying to calm himself down. He had to crush a burning desire to slap the boys for their horrible timing.

As Liz walked back over to them Castle cleared his throat. "That is still a yes for Friday correct?" Castle already knew the answer but he needed to hear her say the word again especially after what had nearly happened.

"Yes Castle. That was a yes." Beckett smiled.

Liz couldn't contain herself and she pulled both of them in for a hug.

"Whoa! Take it easy there. You don't want to end up on the floor again do you?" Castle said which caused Beckett to punch him in the arm. "Ouch! What was that for?"

"That didn't hurt you big baby."

And with that, things went back to normal, or as normal as things ever got with those two anyway.

Later that night, Liz called her uncle to invite him to the Castle's for dinner as well.

"Hi Uncle Jim."

"Hello Lizzie. How is your week with Katie going?"

"It's great so far. I'm really happy to be here now after everything that happened. It's also interesting getting to see her work with Castle. It's funny, she's always really happy when I'm with her, but when he walks into the room, she really lights up."

Jim laughed. He had suspected that there was something more between his daughter and the writer and listening to his niece confirmed his suspicions.

Liz continued "So anyway, I've made friends with Alexis Castle and she's in on my plans this week."

"Why does that sound ominous?"

Liz laughed. "It's not as bad as it sounds. You've met Castle right?"

"Yes. Please tell me you're not planning on doing what I think you are."

"What? You mean like trying to get Kate and Rick to admit their feelings for each other? No, absolutely not Uncle Jim." Liz couldn't keep the grin off of her face. Her uncle was always so intuitive when it came to her and Kate.

"That's what I was afraid of. Listen Lizzy, I really hope you have a good plan because this could end either really well or very badly depending on how you play this."

"I know. That's why I have Alexis, Martha, Lanie and hopefully you on board to help this go well."

"Hang on a second! I never said anything about helping you with your schemes."

"But Uncle Jim, we're counting on you for this to go like we planned. We need all five of us working together for this to work. After all, we are the people who know them the best. And just think about how happy Katie will be if this plan works."

"All right, fine. What do I have to do?"

"As of right now, all you have to do is come to the Castle's loft on Friday night for dinner. Alexis and I are still working on the finer details. I'll let you know specifics on Thursday."

"That sounds easy enough. I'll see you all then."

**AN:  
>Thank you again for reading and don't forget to hit the review button below. :) <strong>


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